Drive train configurations for wind turbines with and without gearbox are well known in the art.
In the first case the gearbox and the generator can be arranged successively as individual components or arranged in a single unit. One example of the latter case is disclosed in U.S. 2006/0104815 A1 in which the generator is constructed as a ring concentrically embracing the gear being both elements axially dismountable and connected in an individually detachable manner to a machine support.
In the second case, particularly in the case of wind turbines having a permanent magnet generator that is directly driven by a connecting arrangement between the rotor hub and the generator, there are known different drive train configurations.
In one of these configurations disclosed in WO 01/94779 A1 the connecting arrangement between the rotor hub and the generator is a two-part axle supported by two bearing units.
In another of these configurations the connecting arrangement between the rotor hub and the generator is a hollow shaft supported by bearings on a tube member (interior to the hollow shaft) attached to the supporting frame of the wind turbine. In these configurations, the wind turbine supporting frame mounted over the tower is designed to permit that the generator unit—having a large-diameter rotor and stator—could be located between the rotor hub and the tower. One example of these configurations is described in U.S. 2004/0108733 A1 in which the hollow shaft is supported by means of a single bearing which also carries moments on the tube member. This configuration is intended to reduce the size and the weight of the elements of the wind turbine which are to be mounted at the top of the tower but has the drawback of a costly maintenance in particular when the dismounting of components is needed.
In another of these configurations, the tower is located between the rotor hub and the generator unit. One example of these configurations is described in WO 02/33254 A1 in which the connecting arrangement between the rotor hub and the generator is a main shaft supported by means of two bearings arranged on a base at the top of the tower.
A problem involved in direct driven drive trains, specially when the tower is located between the rotor hub and the generator unit and consequently requires a long main shaft, is avoiding damaging deformations in the generator unit, when the main shaft bends under high rotor hub loads.
WO 02/033254 addresses that problem by means of a non-rotatable coupling between the generator stator and the wind turbine base. However, this solution involves high bearing loads.
This invention is intended to avoid that drawback.